1. Field of the Invention
The present invention relates to a hybrid vehicle, and relates in particular to a hybrid vehicle that provides protective actions to the power drive unit, which drives the motor.
This application is based on Japanese Patent Application, Unpublished, No. Hei 11-244126, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Conventionally, hybrid vehicles having a motor driven by electrical energy in addition to an engine driven by combustion energy to provide driving force for driving a vehicle are known. One type of such hybrid vehicles is a parallel hybrid vehicle in which the motor is used to assist the operation of the engine as auxiliary driving force. The parallel hybrid vehicle is designed to satisfy driver demands for performance by using the motor to assist the output power of the engine during the acceleration stage, for example, and during the deceleration stage, the motor is used as deceleration regenerator to charge the battery to maintain remaining battery charge (as disclosed in a Japanese Patent Application, First Publication, No. Hei 7-123509, for example).
Hybrid vehicle is provided with a power drive unit for the purpose of motor operation or power regeneration. The power drive unit has a number of switching elements, which are used for controlling the current flow through the motor to drive the motor or regenerate power. A motor control apparatus is provided in such a hybrid vehicle to control the switching elements according to control signals generated by the control apparatus.
Here, if a short circuit develops inside the power drive unit, it is necessary to quickly stop the operation of the switching elements controlling the current in order to prevent damage to the switching elements. Stopping of the current control action using the switching elements may be performed by the motor control apparatus; however, it is necessary to provide a quick remedial action to counter the short circuit problem so that the processing load on the motor control apparatus is increased. For this reason, there is a potential danger that important periodic requirements of the motor, such as torque control for the motor may not be provided by the motor control apparatus in a timely manner.
Furthermore, erroneous determination can be made in checking such short circuit problems so that it is necessary to provide how to process such a situation in the overall control methodology.
It is, therefore, an object of the present invention to provide a hybrid vehicle that, should a short is developed in the power drive unit, can stop control of current to supply power to the switching elements without increasing the processing load on the motor control apparatus.
Another object of the present invention is to provide a hybrid vehicle that can respond appropriately when a detected short in the power drive unit is an erroneous detection.
To achieve the objects, the present invention provides a hybrid vehicle comprising: an engine (engine 1 in the embodiment); a motor (motor 2) which operates with electrical energy; a power drive unit (power drive unit 7) having switching elements to control the flow of current to operate the motor; and a control apparatus (motor control apparatus 5) for generating control signals to operate the switching elements; wherein the power drive unit is further provided with a self-protection circuit (self-protection circuit 75) to interrupt the supply of current to the switching elements temporarily for a specified interval when a temperature of a switching element is higher than a specific temperature value or the value of current flowing through the power drive unit is greater than a specific current value, and to output a signal indicating that the power drive unit is in a self-protection state caused by a current flow interruption; and the control apparatus receives the signal from the self-protection circuit indicating that the power drive unit is in the self-protection state, and if a number of times the signal is received is greater than a predetermined number or if the cumulative time in the self-protection state is greater than a predetermined time, the control apparatus prohibits the control signal from operating the switching elements (steps S21-S29, step S61, step S62).
According to the above structure of the hybrid vehicle, the self-protection circuit included in the power drive unit decides that a shorting state exists based on a condition that either a temperature of the switching elements is higher than a specified temperature value or the value of the current flowing through the power drive unit is greater than a specified current value. When this condition is satisfied, the self-protection circuit temporarily interrupts the control signals to the switching elements for a specified interval. Therefore, when a short is developed inside the power drive unit, current control action of the switching elements can be stopped for a certain period of time.
Accordingly, damage to the switching elements caused by the short can be prevented. Also, because the current control can be provided without going through the control apparatus, rapid remedial response to the short can be provided in a short time.
Also, the self-protection circuit outputs a signal indicating that the power drive unit is in a self-protection state caused by a control signal interruption. Because this interruption of control signals continues for a given duration, if an actual short has been developed, the self-protection state and the non-self-protection state are reported alternately to the control apparatus. Therefore, the control apparatus determines whether the shorting state in the power drive unit is real, according to a number of times the signal is received reaches a predetermined number or the cumulative time in the self-protection state is greater than a predetermined time. When this condition is satisfied, the control apparatus prohibits control signals to the power drive unit.
Accordingly, the control apparatus can distinguish false reporting of shorting from the actual reporting of shorting provided by the self-protection circuit. Therefore, the control apparatus stops the switching elements to perform current control (motor control) completely only when there is an actual short.
In the second aspect of the present invention, the vehicle is further provided with a battery (12 V battery 9) to supply driving power to at least the self-protection circuit and the control apparatus; and the control apparatus stops receiving the signal sent from the self-protection circuit (step S11) when a detected voltage of the battery is lower than a specified voltage value (the voltage-down threshold V1).
The second aspect is important, because when the drive voltage supplied to the self-protection circuit and the control apparatus is low, there is a danger that the operation of the self-protection circuit and the control apparatus becomes unstable such that appropriate response to the shorting state may not be carried out. However, by providing the structure described above, the control apparatus is designed not to detect shorting signals sent from the self-protection circuit so that erroneous detection of shorting state caused by instances of unstable operation can be prevented.
In the third aspect of the invention, the control apparatus prohibits the control signals when the control apparatus sequentially detects, at a predetermined duration (specified duration T4), a condition that either a number of times the signal is received is greater than a predetermined number or the cumulative time in the self-protection state is greater than a predetermined time (steps S31-S36).
Accordingly, it is possible to prevent erroneous confirmation of the shorting state caused by a short break of power supplied to the power drive unit.
In the fourth aspect of the present invention, the control apparatus decides that the battery is in a voltage-low state when a state, in which the detected voltage of the battery is lower than the specified voltage value, continues for a specified voltage-low determination interval (voltage-low determination interval A2), and responds by lowering an existing value of the motor torque to zero or by prohibiting the control signals depending on the operating conditions of the motor (steps S65-S68).
Accordingly, in the voltage-low state of the battery in which there is a fault in the battery power supply system, it is possible to stop control actions of the motor safely before the supply of driving power becomes completely exhausted.
Also, according to the fifth aspect of the present invention, the control apparatus determines that the battery that had been in a voltage-low state is now in a voltage-recovery state when a state, in which the detected voltage of the battery is higher than a specified threshold value (voltage-up threshold Vh), continues for a specified voltage-recovery determination interval (voltage-recovery determination interval B2), and responds by outputting a control signal to operate the motor so as to adjust an existing value of the motor torque to match a demanded value of the motor torque (steps S69-S72).
Accordingly, although the determination had been made that the battery is in the voltage-low state, if in reality, there is no fault in the battery power supply system and the battery voltage is restored, the normal operation of the vehicle can be resumed.